Family members are charged with the first-degree murder of three sisters and a female caregiver who were found dead in a car submerged in the Rideau Canal near Kingston last month.

The girls' parents, Mohammad Shafia and Tooba Yahya Mohammad, along with their 18-year-old son, Hamed Mohammad-Shafia, are all charged with four counts of first-degree murder and conspiracy to commit murder.

Police said at least one of the accused had plans to travel to a foreign country. All three were arrested in Montreal on Wednesday.

The bodies of Zainab Mohammad-Shafia, 19, Sahar, 17, Geeti, 13, and Rona Amir Mohammad, 52, were pulled from a Nissan Sentra that was submerged in about three metres of water in the Rideau Canal on June 30. Police are not releasing the causes of death.

Police said the accused all attended the Kingston police station on June 30 to report the family missing. Although Mohammed Shafia initially told investigators that the 52-year-old woman was his cousin, police later learned she was his first wife.

A news conference to update the media on the investigation on Thursday started with a brief moment of silence in memory of the victims.

Kingston police Chief Stephen Tanner told reporters he was saddened at the "needless and senseless loss of innocent human lives."

"The four victims in this case, three of which were only teenaged girls, all shared the rights within our great country - to live without fear, to enjoy safety and security, and to exercise freedom of choice and expression - and yet had their lives cut short by members of their own family," he said.

The family is from the north-end Montreal borough of St-Leonard. They were on their way home from a vacation to Niagara Falls, Ont. Police said they ended up in Kingston on June 30 when they decided to stop at a motel in the early morning hours.

Police said the family was travelling in two vehicles, a Nissan Sentra and a Lexus SUV. Both vehicles are being examined by investigators.

As a result, police said they've been able to link the SUV and the three accused to the crime scene.

Early in the investigation, the deaths appeared to puzzle investigators as they pieced together how the car plunged into the canal at the location where it was found.

The vehicle would have had to pass over rocks and a curb. It also would have had to get through a gate that was closed.

Police also couldn't find significant tire marks, which would have been consistent with a case of reckless driving.

Although none of the victims had a driver's license, police said all three of the accused told investigators that Zainab, the eldest daughter, had a tendency to take the family vehicle without consent.

Days after the deaths, the girls' father told reporters the same thing, saying he believed the tragedy happened after Zainab got behind the wheel.

Now, police have been able to determine the scenario described by the girls' family did not happen.

"Our investigation to date reveals that this particular allegation is false and that on the night in question, the vehicle was operated by a combination of the three accused persons," said Insp. Brian Begbie, who led the investigation.

The family moved to Canada two years ago. The girls were born in Afghanistan and have three other siblings. Those children are currently in the care of child protective services.